Smartphone Battery Myths, Explained

Over just a few years, the batteries in our smartphones have changed a lot. That means those old tips to stretch out your battery life just aren't as true as they once were, yet we still share them like they're gospel. Before telling someone to disable Bluetooth or Wi-Fi, let's shed some light on those old myths.

Illustration by Sam Wooley

Myth: You Should Completely Discharge Your Battery Before Plugging It In

Batteries used to be stupid. Older batteries would "forget" their full capacity, so they wouldn't be able to fully charge again. So, you'd have to let a battery discharge all the way to 0% before charging it again. That's not the case anymore, and it hasn't been for a long time.

Smartphones today have lithium-ion batteries, which don't suffer from the memory problems of older nickel cadmium and nickel-metal hydride batteries. Similarly, lithium-ion batteries count charges differently than older batteries, so you don't need to worry about discharging it completely. Here's how Apple explains it, and while they reference their batteries, the rules apply to any lithium-ion battery:

Charge your Apple lithium-ion battery whenever you want. There's no need to let it discharge 100% before recharging. Apple lithium-ion batteries work in charge cycles. You complete one charge cycle when you've used (discharged) an amount that equals 100% of your battery's capacity -- but not necessarily all from one charge. For instance, you might use 75% of your battery's capacity one day, then recharge it fully overnight. If you use 25% the next day, you will have discharged a total of 100%, and the two days will add up to one charge cycle. It could take several days to complete a cycle. The capacity of any type of battery will diminish after a certain amount of recharging. With lithium-ion batteries, the capacity diminishes slightly with each complete charge cycle. Apple lithium-ion batteries are designed to hold at least 80% of their original capacity for a high number of charge cycles, which varies depending on the product.

Most manufacturers still suggest you "calibrate" your battery by discharging and recharging it once every one to three months. Since your battery's overall life diminishes over time, the time you have left on each full charge decreases a little with every full discharge. Essentially, every discharge shortens the battery life just a little bit. Discharging to 0% once a month helps the operating system calibrate the full life cycle of the battery so it knows exactly how much it has diminished over time.

However, more and more batteries have a digital calibration tool built into them. These "smart batteries" supposedly reduce the need to calibrate, though it's still recommended when your battery behaves oddly. If you see the battery percentage on your phone jump around a lot (like you could have sworn it was fully charged, and now it's at 20%,) it's time to calibrate it. You don't want to do this too often though. It's actually bad for lithium-ion batteries to be regularly drained all the way to 0%. That counts as a full charge cycle, which in turn decreases the battery's total life.

In the same vein as calibrating your battery, it used to be possible to ruin a battery by "overcharging," or leaving it plugged in all the time. When you plugged in your phone for long periods, older lithium-ion batteries could overheat (or explode, in rare cases), which in turn just reduces the charge capacity and long-term life of the battery (this can still happen if you have a case that doesn't allow for heat to dissipate).

Something that's not an issue is overcharging. Contrary to what you might think (or have been told), leaving your phone or laptop plugged in all the time is not bad for its battery. That's because your gadgets, the batteries in them, and the chargers you attach them to are actually pretty smart about the way they do business. Trickle charge -- what your battery gets when it's connected and full -- is way less detrimental to the battery's health than a larger discharge would be.

That said, leaving your phone plugged in all the time can still lead to degradation, but it's not enough that you'll even notice. As we've pointed out before, if you want to extend the life of your battery, you want to keep it between 40%-80% all the time. That sounds great on paper, but it's pretty ludicrous for someone living in the modern world. The good news is leaving it plugged in overnight while you sleep, even if it's close to full, doesn't negatively affect it as much as it used to.

This is also a good time to point out that taking care of your smartphone's battery is a little different than something like a laptop for one simple reason: you probably get a new phone at least every two years. The lifecycle of that battery isn't as important as it used to be because the lifespan of a phone is so short. Of course, you may be the type to hold onto a phone forever,, but if you're not, worrying about this stuff is unnecessary. Batteries will die and degrade over time no matter what you do, so don't obsess over it too much.

Myth: Closing Apps Improves Battery Life

We like to think of our smartphones as little computers, and we treat them like so. On your laptop, having a bunch of apps open at once -- especially ones that connect to the internet -- strains your battery, so it makes sense that your smartphone would work the same way, right? Wrong. That's not how smartphones work.

In the case of iOS, apps do not stay open the same way they do on a computer. When you leave an app, it's frozen, doesn't do anything, and doesn't require any resources. Closing them does nothing for your battery -- except it costs CPU power and battery to close everything. Former Genius Bar technician Scotty Loveless explains:

By closing the app, you take the app out of the phone's RAM. While you think this may be what you want to do, it's not. When you open that same app again the next time you need it, your device has to load it back into memory all over again. All of that loading and unloading puts more stress on your device than just leaving it alone. Plus, iOS closes apps automatically as it needs more memory, so you're doing something your device is already doing for you. You are meant to be the user of your device, not the janitor.

The same is true for Android. You'll hear some people swear by task killers to handle close apps and improve battery life. The problem is, they don't work, and do more harm than good. Similarly to iOS, when you kill a task on Android, you'll just have to restart it again, and doing so puts drain on the CPU, which puts drain on the battery. Whether you're manually killing apps or using a task killer, you're using resources you otherwise wouldn't be, and that kills the battery.

Instead of closing apps all the time, it's better to turn off background data when you can. On iOS, it's called Background App Refresh. This means apps can load data in the background, even when it's not in focus. When they do this, they use CPU power, which drains the battery. You can prevent apps from doing this by heading to Settings > General > Background App Refresh and change the toggle for any apps you don't care about. On Android, you can turn off background data by heading to Settings > Wireless & networks > Data usage and set "Allow background data" to "Restrict background data." However, be warned that while it will save you battery life, some apps, like the Play Store, simply won't work at all with the background data restricted.

All this isn't to say that apps aren't the problem. Certain software, like messaging apps, absolutely destroy your smartphone's battery life. So, turn off Background App Refresh for apps that don't need it, disable notifications for apps that have no business notifying you, and delete any apps you're not actually using. Apps can still kill your battery if they're poorly programmed or just extremely demanding. Smartphones also now have great metrics so you can track which apps are doing so. On Android, you can head to Settings > Battery to see which apps are using the most power. On iOS, head to Settings > Battery to see similar information.

Modern USB chargers are standardised and while you'll see different charge time results with different chargers, that doesn't affect the battery itself at all. Ken Shirriff took a look at various chargers a number of years ago and found that while the time it takes to charge a device varied from charger to charger, doing so with a third-party charger has no effect on the battery itself. That includes using chargers that supply a different number of amps than the phone expects. Modern smartphone batteries are smart enough to only use the maximum amount of power it can handle regardless of what being supplied, so there's no danger of overheating as long as the charger itself is providing the correct current. Knockoff chargers often pretend to supply more (or less) power than they should (or vary wildly even during a charging session,) which is where the trouble comes in. Off-brand chargers won't do this.

It seems like every new feature added to smartphones, whether it's Background App Refresh in iOS or Google Now On Tap on Android, is a serious threat to your smartphone's battery life. While that's true, you don't have to go through and toggle every new thing to "Off,", nor is there any use in disabling basic system services like Bluetooth or Wi-Fi just to save battery.

For example, MacWorld took a look at the toll system services take on an iPhone's battery and found that many don't have a huge effect. For example, leaving location services on for an app you're not actively using has almost no effect on the battery life whatsoever. Similarly, turning on Aeroplane Mode, which cuts cellular, Wi-Fi, Bluetooth, GPS, and location services, only squeezed out an extra 30 minutes of life, which isn't that much all things considered (and this was two years ago, things have likely improved since then). Wi-Fi and Bluetooth used to draw a lot of power, but nowadays they draw so little that toggling them on and off does little for your battery life. Of course, if you don't use Bluetooth or Wi-Fi, just leave them off, but don't feel like you have to do so.

What usually kills your battery the fastest is the screen. So if you're really worried about battery life, just turn the screen off and put the phone in your pocket until you really need to use it.

This is the same issue as the first Myth in the article. Older nickel cadmium and nickel-metal hydride batteries needed to be fully charged before being used, but that doesn't apply to newer lithium-ion batteries.

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